Is it my imagination, or have they turned down the volume of the pre-recorded muezzin calls in Turkey this year? Perhaps it is only that my hearing has grown less acute with age. After all, I learned that I was short-sighted many years ago by complaining at a clinical pathology conference that the pathology slides shown were nothing but a pink and blue blur, having assumed that the problem was with the slides rather than with my eyes. The subject of my talk in Turkey was the social changes in Britain discernible from a comparison of the crime novels of Agatha Christie and Ian Rankin. I accept that there was nothing scientific about my method – it was like trying to examine the effects of the French Revolution by comparing Molière with Céline – but all the same I couldn’t help feeling that there was something to my approach. For example, one couldn’t imagine either Hercule Poirot or Miss Marple chewing gum, as Rebus does, or taking gum out of their mouths and dropping it on the pavement, as Rebus also does. Neither could I imagine either of Agatha Christie’s sleuths listening, like Rebus, to the music of a band called Spooky Tooth.